webshare: Small refactor of WebShare (OnceCallback, const&, and alias)

chrome/browser/ui/browser_dialogs.h

Index: chrome/browser/ui/browser_dialogs.h
diff --git a/chrome/browser/ui/browser_dialogs.h b/chrome/browser/ui/browser_dialogs.h
index e82786079f6c931ae562f9a175afe233d9f37b7a..e1bd574bbe12e1c5443c4bc362d49d2a39583f6d 100644
--- a/chrome/browser/ui/browser_dialogs.h
+++ b/chrome/browser/ui/browser_dialogs.h
@@ -73,6 +73,11 @@ class WebDialogDelegate;
 
 namespace chrome {
 
+// Used by ShowWebShareTargetPickerDialog to return the target the user picked
+// or nullopt if the user cancelled the share.
+using WebShareTargetPickerCallback =
+    base::Callback<void(const base::Optional<std::string>&)>;

[Matt Giuca, 2017/05/01 06:50:06]

I think this should go at the bottom of the file -- see how there is a similar
one called IntentPickerResponse. Just make sure it goes outside of the ifdef
CHROMEOS.

[ortuno, 2017/05/01 07:13:02]

As discussed the alias has to be defined before it's used i.e. before
ShowWebShareTargetPickerDialog.

[sky, 2017/05/01 21:08:50]

optional: put this right above the the single place it's used.
optional2: use OnceCallback.

[ortuno, 2017/05/01 22:55:00]

Done. Q: Is it usually just a judgement call where to put the alias? The style
guide says to put it at the top of the file with other types[1] but I've seen
instances of them being defined right above where they are used[2].
Done.

[1] https://google.github.io/styleguide/cppguide.html#Declaration_Order
[2]
https://cs.chromium.org/chromium/src/device/bluetooth/bluetooth_device.h?sq=p...

+
 // Shows or hides the Task Manager. |browser| can be NULL when called from Ash.
 // Returns a pointer to the underlying TableModel, which can be ignored, or used
 // for testing.
@@ -164,7 +169,7 @@ payments::PaymentRequestDialog* CreatePaymentRequestDialog(
 void ShowWebShareTargetPickerDialog(
     gfx::NativeWindow parent_window,
     const std::vector<std::pair<base::string16, GURL>>& targets,
-    const base::Callback<void(base::Optional<std::string>)>& callback);
+    const WebShareTargetPickerCallback& callback);
 
 #if defined(OS_MACOSX)